The present invention relates to a photographic film cassette, and more particularly to an improved self-advancing film cassette capable of initially advancing the film smoothly by rotating the spool.
In a camera for use with 135 film, unexposed photographic film is drawn from a film cassette for each exposure, positioned on an exposure aperture, and wound up in a film take-up chamber. When no further wind-up can be carried out, a rewinding shaft provided in a film loading chamber of the camera rotates the spool to rewind the film in the cassette shell. For this purpose, a recess is formed on an end of the spool for fitting the spool end on a fork formed on the rewinding shaft. A pair of projections are formed inside the recess for rotating the spool in contact with the fork. In a conventional film cassette with a roll of 135 mm film contained therein, a leader of the film protrudes from the cassette shell. When the film cassette is loaded in the camera, the cassette shell is inserted in the film loading chamber while the film leader is treated carefully to be positioned appropriately along a film passageway in the camera.
Film cassettes for simplifying the loading operation have been proposed recently, as disclosed in U.S. Pat. No. 4,846,418 and 4,834,306. In such film cassettes, the film leader is contained completely in the cassette shell, and can be advanced outside the cassette shell by rotating the spool. According to U.S. Pat. No. 4,846,418, annular ridges are formed on the inside of the cassette shell to contact the outermost turn of the wound film so as to prevent the film from loosening around the spool.
In such a film cassette, which requires no treatment of the film leader while loading the cassette in the camera, there is a necessary construction to connect the film passage mouth appropriately to a film passageway along the exposure aperture. Thus, the cassette shell must be positioned precisely in the film loading chamber. It is known already from Japanese Utility Model Laid-Open Publication No. 49-75340 and Japanese Patent Laid-Open Publication No. 63-184750 to position the cassette shell correctly in the film loading chamber by forming a positioning portion on the cassette shell to contact a receiving member formed on the inside of the film loading chamber.
However, there is a problem with a self-advancing film cassette in which the outermost turn of the film is in contact with the annular ridges. If the spool is deviated axially from the rewinding shaft of the camera, the rotation of the spool causes the annular ridges to press excessively or scratch a part of the outermost turn of the film. The film leader might not be advanced because the sliding friction is greater.
According to known constructions for positioning the film cassette in the film loading chamber, there also is the problem of low precision. Errors in assembly cause deviation in connecting the film passage mouth to the film passageway, because the positioning portion is formed on a shell component different from that having a film passage mouth according to the disclosed construction.